The phytochemical indole-3-carbinol (I3C), found in cruciferous vegetables, and its major acid-catalyzed reaction product 3, 3′-diindolylmethane (DIM) showed anti-cancer activity mediated by its pleiotropic effects on cell cycle progression, apoptosis, carcinogen bioactivation and DNA repair. In order to further elucidate the molecular mechanism(s) by which DIM exerts its effects on breast cancer cells, we have utilized microarray gene expression profiling analysis. We found a total of 1,238 genes altered in DIM-treated cells, among which 550 genes were down regulated and 688 genes were up-regulated. Clustering analysis showed significant alterations in some genes that are critically involved in the regulation of cell growth, cell cycle, apoptosis and signaling transduction including down-regulation of survivin. Previous studies have shown that anti-apoptotic protein survivin is over-expressed in many human cancers including breast cancer. However, very little or no information is available regarding the consequence of down-regulation of survivin for cancer therapy. We therefore hypothesized that down-regulation of survivin as observed by DIM could be an important approach for the treatment of breast cancer. We have tested our hypothesis using multiple molecular approaches and found that DIM inhibited cell growth and induced apoptosis in MDA-MB-231 breast cancer cells by down regulating survivin, Bcl-2 and cdc25A expression and also caused up-regulation of p21WAF1expression which could be responsible for cell cycle arrest. Down regulation of survivin by siRNA prior to DIM treatment resulted in enhanced cell growth inhibition and apoptosis while over-expression of survivin by cDNA transfection abrogated DIM-induced cell growth inhibition and apoptosis. These results suggest that targeting survivin by DIM could be a new and novel approach for the prevention and/or treatment of breast cancer.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]